This invention relates to a phased array radar antenna and in particular to a two-stage time delay steered architecture whereby a first time delay stage is provided at the subarray level and a second time delay stage is provided at the radiating element level.
The use of time delay units for one-stage time steered subarrays of a phased array antenna is well known in the art and described in the Radar Handbook, M. I. Skolnik, Editor, McGraw-Hill, New York, 1970, Section 11.6. In a paper by J. [rank titled "Bandwidth Criteria for Phased Array Antennas," published in Phased Array Antennas, Oliver and Knittel, Editors, Artech House, Inc., 1972, it states on p. 247 that although a time delay network at each element of an array is prohibitively costly with present microwave techniques, a marked increase in instantaneous bandwidth can be obtained using subarrays with time delay networks by dividing the aperture into subapertures or subarrays and placing a time delay network behind each subarray.
Traditional phased arrays use phase shifters at the element level for antenna beam steering and time delay units (TDU) at the subarray level for high range resolution in wideband modes. However, in certain radar applications there is a need for low two-way (transmit/receive) attenuation at the instantaneous bandwidth edges for high signal-to-noise ratio (SNR) in order to obtain greater details on radar targets at longer range. Another array may be used instantaneously over a narrow band, but it may be desirable to hop from frequency-to-frequency without resetting the phase shifters. Hence, when using the traditional one-stage subarray time steering, the normal subarray size required for range resolution needs to be reduced to obtain high signal-to-noise (SNR) in wide band and wide scan mode. Consequently, the number of subarray TDUs and their related power combining networks increase. For example, in an array comprising 25,344 elements, 176 subarrays (each subarray having a 6-bit TDU) would be required to meet a range resolution requirement of 15 cm. However, to meet a two-way bandwidth attenuation requirement of 4 dB, the array would require 704 subarrays, each with a 6-bit TDU, and their related power combining networks, but such a system is very expensive.